The aim of the research is to first study the subpopulations of T-cells, generated in response to infection with a non-virulent strain of Plasmodium yoelii. The ability of purified subpopulations of T-cells from spleens of immune mice to adoptively transfer anti-malaria immunity to T-cell deficient and normal mice will be examined. Experiments will be done in vivo to directly determine whether these protective T-cells function exclusively as "helper" cells in the production of protective antibodies by B-cells, or whether protective T-cells perform another role(s) in the expression of immunity. Experiments will also be done to determine if purified B-cells from immune mice can adoptively transfer immunity to T-cell deficient recipients. The immune response of animals to infection with a virulent strain of P. yoelii will also be examined. Specifically, it will be determined if there are defects in the hosts cellular response to virulent infection or if a suppressor mecahnism(s) interferes with the successful generation and expression of anti-malaria immunity.